Small Amounts Of Iron Research Articles

1094.ジルコニウム合金の均一腐食および水素吸収に及ぼす析出物の電気化学的役割,(I)

Substantial roles of precipitates such as Zr-Fe-Cr type intermetallic compounds on uniform corrosion and hydrogen pickup of zirconium alloys in pure water autoclave tests were investigated from an electrochemical point of view. This paper describes the roles on corrosion. A corrosion test on precipitate-containing and precipitate-free materials made from pure zirconium and a small quantity of iron and chromium, rest potential measurements on an intermetallic compound of Zr(FeCr)2 and zirconium matrix, and a galvanic coupling test of those were performed. Results showed that corrosion behavior of zirconium alloys could be attributed to the electrochemical properties of intermetallic compounds precipitated in each alloy. Namely, the cathodic and anodic polarization characteristics were associated with anodic protection provided by the precipitates on the alloys and the precipitates degradation in the oxide films, respectively. The mechanism was confirmed through a corrosion test of Zr-X(X=0.2Fe, 0.2Cr, 0.1Fe-0.1Cr) alloys and electrochemical measurements of ZrFe2, ZrCr2, and Zr(FeCr)2 intermetallic compounds.

Catalytic wet oxidation with H 2O 2 of carboxylic acids on homogeneous and heterogeneous Fenton-type catalysts

The catalytic wet oxidation with hydrogen peroxide (WHPO) of diluted formic, acetic and propionic acid solutions (total organic carbon of 30 mg C/l) in the 25–70°C temperature range using a Fe 3+-containing zeolite (Fe/ZSM5) is compared with the behavior of homogeneous Fe 3+ catalysts at the same experimental conditions. Although the heterogeneous catalysts have a higher reactivity and a reduced dependence on the pH of the solution in comparison to the homogeneous Fe 3+ catalysts, they also have a higher rate of the side reaction of hydrogen peroxide decomposition to water and oxygen. Leaching tests indicate that the activity of the heterogeneous catalyst is not due to leached iron ions, although a small amount of iron was found in the aqueous solution. It was also observed that catalytic behavior could be reproduced in consecutive catalytic experiments, but an intermediate calcination step is necessary to oxidize the organic species which remain trapped inside the pore of the zeolite.

Galvanomagnetic Effect of Graphite Mixed with Iron and Heat-treated at High Temperatures

Graphite films prepared from aromatic polyimides and a3000°C-treated grafoil were mixed with iron and heat-treated up to 2700°C and/or above. Effects of iron on the transverse magnetoresistance Δρ/ρ0, Hall coefficient RH and residual resistivity ratio RRR of these iron-doped graphite materials have been investigated. RH data imply that only a small amount of iron can substitute into the graphite lattice irrespective of the crystal perfection, and act as acceptors and impure. The heat treatment of graphite materials mixed with iron induces a decrease of Δρ/ρ0 and RRR for the original specimens with RRR>4, but an increase for those with RRR<4. These results indicate that the improvement of crystallinity of graphite materials through a catalytic action of iron becomes predominant for the specimens with RRR<4.

X-ray diffraction, 57Fe Mössbauer and step potential electrochemical spectroscopy study of LiFeyCo1−yO2 compounds

Abstract With the aim of finding new cathode materials for lithium-ion batteries, the synthesis of layered solid solutions with LiFeyCo1−yO2 stoichiometries has been studied in this work. X-ray single phase products were obtained by a ceramic procedure for 0≤y≤0.2. The unit cell dimensions of the powdered solids increase with the iron content. The Rietveld analysis of a sample with y=0.1 using anisotropic thermal parameters led to RBRAGG=3.37. The hexagonal unit cell parameters of this solid were a=2.8271(1) A and c=14.1266(7) A. The site occupancy used in the Rietveld procedure was: (FeT0.0086)6c[Li0.9868FeO0.0046]3b[Li0.0132Co0.9000FeO0.0868]3aO2 according to the intensity of the signals observed in the Mossbauer spectrum. This consists of one intense (87%) quadrupole split signal with isomer shift of ca. 0.316(3) mm/s is ascribable to Fe(III) replacing cobalt in the CoO2 layers. Two weaker quadrupole signals result from small amounts of iron in octahedral 3b and pseudotetrahedral 6c sites of the LiO2 layers. The presence of pseudotetrahedral iron puts obstacles to the lithium ion diffusivity. In consequence, the electrochemical spectra evidence an increased cell polarization as increases. The lithium extraction at the end of the first charge decreases with iron content, with a maximum of 0.6 Li per formula for y=0.1. The introduction of nickel in the composition of these solids may be useful to improve the electrochemical performance of the solid solutions. Ternary systems show an improved electrochemical behaviour.

Novel Catalytic Oxidative Synthesis of Soluble Conductive Polymers of Poly(3-butoxycarbonyl-4-methylpyrrole)

Abstract A soluble conductive polymer, poly(3-butoxycarbonyl-4-methylpyrrole) was synthesized by catalytic oxidative polymerization of 3-butoxycarbonyl-4-methylpyrrole, where only a small amount of iron (III) chloride as a catalyst, and enough amount of oxygen as an oxidant were used. Addtion of BF3·Et2O to the reaction system can make the yield of the polymer remarkably increase.

Structure et propriétés magnétiques du composé NH4Fe3(H2PO4)6(HPO4)2,4H2O

The title compound is prepared by adding aqueous ammonia to a solution of phosphoric acid containing a small amount of iron (III) ions (3%). It crystallizes in the monoclinic system, space groupC2/c,a=16.8450(9) Å,b=9.6111(1) Å,c=17.6470(7) Å, andβ=90.91(2)°,R=0.031, and wR=0.078. The structure consists of a two-dimensional framework made of HPO4, H2PO4groups, and FeO6octahedra sharing corners. In one layer, the NH+4cations are located inside 12 membered windows, which are generated by the corner-sharing FeO6and H2PO4. Water molecules lay in the interlayer space. With regard to magnetic properties, carried out in the range 1.7–300 K, the polycrystalline sample follows a Curie–Weiss law down to 30 K. At lower temperatures is a magnetic phase transition, where a spontaneous magnetization appears. This behavior suggests either a ferrimagnetic or a weak ferromagnetic order.

Preparation of FeMnB Alloys by Chemical Reduction

Iron-manganese alloys are of fundamental interest in their amorphous form due to their re-entrant spin glass behavior [1], and in the crystalline form as the host system for shape-memory devices [2]. The most common routes to amorphous alloys are melt spinning, mechanical alloying, and rf sputtering. However, in the last decade, a chemical synthesis route to amorphous alloys has been utilized to prepare a variety of nanoscale materials, including alloys of FeB [3], FeCoB [4], FeNiB [5], FeCuB [6], FeWB [7] and FeNiPB [8]. The reaction involves the reduction of an aqueous solution of metal salts by aqueous sodium borohydride. Control of the product composition may be achieved by changing the molar ratios of the precursors; and other properties, including particle size and the degree of amorphicity or crystallinity, may be varied by changing the reagent concentration, the reaction pH, or the addition rate of the reagents. In this letter, we present the ®rst results of a study of the preparation of amorphous FexMnyB alloys by chemical reduction. The synthesis of FexMnyB alloys was performed using argon-purged solvents via the reduction of a solution (200 ml) containing iron (II) sulphate heptahydrate (8.92 g, 32.0 mmol) and manganese (II) sulphate tetrahydrate (0.89 g, 4.0 mmol) by the dropwise addition of aqueous sodium borohydride (1.13 g, 30.0 mmol, 200 ml), yielding a black precipitate accompanied by the evolution of hydrogen gas: 3BH4 ‡ 2M2‡ ‡ 2H2O! 2MB‡ BO2 ‡ 2H‡ ‡ 7H2 (1) During the process, the pH was maintained at 5.5 by the addition of aqueous sodium hydroxide. Control of the pH of the reaction is critical for minimizing impurities in the alloy. After performing a series of reactions at different pH, we found that a pH of 5.5 gave the best results with products that contained minimal impurities. Following precipitation, the samples were washed with water (7 1) to remove any unreacted starting materials, and then stored in an argon glove box to help limit oxidation. A compositional analysis of the samples was performed using electron microprobe analysis (EMA) to determine the iron to manganese ratio, and atomic absorption spectroscopy (AAS) was done to determine the iron to boron ratio. An EMA line scan (1 im spots at 6 im intervals) showed little deviation in the iron to manganese ratio (8.1:1), which agreed with the 8:1 ratio used in the reaction. The EMA data are similar to that of a FeNiB alloy, prepared by us, that is known from the work of earlier researchers to contain a single amorphous phase when prepared by chemical reduction [5]. Combining the EMA and AAS data gives Fe57 Mn7B36 as the overall composition for the product. The morphology of the samples was investigated by scanning electron microscopy, which revealed roughly spherical grains of ca. 200 nm diameter. They agglomerated into larger particles without regular shape, ranging from 2 im to 30 im in size. The structural properties of the product was probed using X-ray powder diffraction, Fe MoEssbauer spectroscopy, and differential scanning calorimetry. The X-ray diffraction pattern (Fig. 1) shows two broad peaks at 208 and 348, characteristic of an iron-based amorphous alloy [9]. A detailed inspection of the X-ray diffraction data indicates minor crystalline peaks corresponding to Fe2O3. Small quantities of iron (III) oxide impurities are often seen in chemically prepared amorphous alloys. Nanophase amorphous alloys are always oxygensensitive, in some cases violently, and invariably require surface oxygen passivation. The Fe MoEssbauer spectrum (Fig. 2) consists predominately of a broad magnetic sextet, typical of an amorphous material, which accounts for 97:5 1:0% of the total spectra area. This component

57Fe MÖssbauer spectroscopy of intermetallic phases in D.C. cast aluminium

Direct-chill (D.C.) casting is a widely used technique for casting industrial aluminium alloy ingots. Commercial purity alloys contain small amounts of iron and silicon. During casting, intermetallic phases are formed inter-dendritically from the final liquid to solidify. Since the solidification rate varies substantially with position in the ingot various phases can form, ranging from the equilibrium phase Al{sub 3}Fe{sub 4}, to increasingly metastable phases, such as Al{sub 6}Fe, Al{sub x}Fe, Al{sub m}Fe or alpha-AlFeSi, as the solidification rate increases. The phases formed may influence the ease of processing and the final gauge properties of the material. Fe Moessbauer spectroscopy has been used previously to identify the intermetallic phases in situ in aluminium from Bridgman grown model alloys. Also variable temperature studies have been carried out on the phases extracted from the alloys by butanol dissolution. The work reported in this paper demonstrates how the Moessbauer data obtained from the previous studies can now be used to identify and quantify the proportion of different phases formed in ingots prepared by direct-chill casting and subsequent heat treatments.

Prevention of iron-deficiency anemia: Comparison of high- and low-iron formulas in term healthy infants after six months of life

Objectives: For bottle-fed babies or nursing infants who receive milk supplements, the American Academy of Pediatrics recommends the use of iron-fortified infant formula. Because these recommendations have not been universally adopted, the hematologic effects of currently available low-iron formulas need to be determined. Study Design: Healthy Chilean 6-month-old infants (without iron-deficiency anemia, born at term weighing ≥ 3.0 kg) who were totally or partially weaned from the breast were randomly allocated in a double-blind fashion to receive high-iron ( n = 430) or low-iron formula ( n = 405), containing an average of 12.7 mg/L or 2.3 mg/L, respectively, of elemental iron as ferrous sulfate. Iron status was determined at 12 months. Results: The prevalence of iron-deficiency anemia was not different in the high- and low-iron groups (2.8% versus 3.8%, p = 0.35). Nevertheless, infants receiving high-iron formula had somewhat higher levels of hemoglobin and serum ferritin, greater mean cell volumes, and lower erythrocyte protoporphyrin levels ( p < 0.005). Conclusions: Although high-iron formulas are more efficacious in improving iron status, currently available low-iron formulas may prevent iron-deficiency anemia in selected healthy, term infant populations with otherwise poor sources of dietary iron after 6 months of life. Formulas with relatively small amounts of iron appear to prevent iron-deficiency anemia. We speculate that the optimal level of iron fortification likely lies somewhere between the current levels in high- and low-iron formulas. (J Pediatr 1998;132:635-40.)

Crystal Structure Refinement and Stability of LaFexNi1−xO3Solid Solutions

The crystal structure refinement of LaFexNi1−xO3(0≤x≤1) solid solutions was determined and analyzed by means of Rietveld refinement from X-ray powder diffraction data. The solid solutions with 0≤x<0.5 are isostructural with LaNiO3and crystallize in the rhombohedral system, space groupR3c, while those with composition 0.5<x≤1 are isoestructural with LaFeO3and crystallize in the orthorhombic system, space groupPnma. All of the solutions are single phase except that with the intermediate composition (x=0.5), where both phases are observed. The cell volume increases with the iron content. This can be ascribed to the larger ionic radius of Fe3+(HS) compared to Ni3+(LS). LaFe0.25Ni0.75O3was found to be single phase when prepared at temperatures as high as 1000°C, indicating an increase in the stability of the perovskite phase at high temperatures when a relatively small amount of iron is substituted for Ni in LaNiO3.

Core formation and chemical equilibrium in the Earth—I. Physical considerations

Current models of planetary formation suggest a hierarchy in the size of planetesimals from which planets were formed, causing formation of a hot magma ocean through which metal-silicate separation (core formation) may have occurred. We analyze chemical equilibrium during metal-silicate separation and show that the size of iron as well as the thermodynamic conditions of equilibrium plays a key role in determining the chemistry of the mantle (silicates) and core (iron) after core formation. A fluid dynamical analysis shows that the hydrodynamically stable size of iron droplets is less than ∼ 10 −2 m for which both chemical and thermal equilibrium should have been established during the separation from the surrounding silicate magma. However, iron may have been separated from silicates as larger bodies when accumulation of iron on rheological boundaries and resultant large scale gravitational instability occurred or when the core of colliding planetesimals directly plunged into the pre-existing core. In these cases, iron to form the core will be chemically in dis-equilibrium with surrounding silicates during separation. The relative role of equilibrium and dis-equilibrium separation has been examined taking into account of the effects of rheological structure of a growing earth that contains a completely molten near surface layer followed by a partially molten deep magma ocean and finally a solid innermost proto-nucleus. We show that the separation of iron through a completely molten magma ocean likely occurred with iron droplets assuming a hydrodynamically stable size (∼ 10 −2 m) at chemical equilibrium, but the sinking iron droplets are likely to have been accumulated on top of the partially molten layer to form a layer (or a lake) of molten iron which sank to deeper portions as a larger droplet. The degree of chemical equilibrium during this process is determined by the size of droplets which is in turn controlled by the size and frequency of accreting planetesimals and the rheological properties of silicate matrix. For a plausible range of parameters, most of the iron that formed the core is likely to have been separated as large droplets or bodies and chemical equilibrium with silicate occurred only at relatively low temperatures and pressures in a shallow magma ocean or in their parental bodies. However, a small portion of iron that separated as small droplets was in chemical equilibrium with silicate at high temperatures and pressures in a deep magma ocean during the later stage of core formation. Therefore the chemistry of the core is mostly controlled by the chemical equilibrium with silicates at relatively low temperatures and pressures, whereas the chemistry of the mantle controlled by the interaction with iron during core formation is likely to have been determined mostly by the chemical equilibrium with a small amount of iron at high temperatures and pressures.

Recycling. Recovery of Nickel and Cobalt from Spent Catalyst by Means of Solvent Extraction with Synergistic Mixtures of Picolylamine in Combination with DNNSA.

The total dissolution of spent hydrodesulfurization catalyst (HDS) in sulfuric acid yields an acidic solution containing a certain amount of rare metals like molybdenum, vanadium, cobalt, nickel, and a small amount of iron as well as large excess of aluminum. In order to recover Co and Ni from the raffinate after the selective extraction of Mo and V with phosphinic acid extractants such as CYANEX 272 and PIA-8, a systematic investigation was conducted on the synergistic extraction with the mixed solvents consisting of dinonylnaphthalenesulfonic acid (DNNSA) and a series of N-alkyl-bis-picolylamine such as tri-decyl-picolylamine (TDPA), oleylpicolylamine (OLPA), and octa-decyl-picolylamine (ODPA). It was elucidated that all of these mixtures could exhibit a good synergistic effect for the extraction of Co, and Ni, while, the extraction of Al was considerably suppressed. In particular, the mixture of TDPA, or OLPA in combination with DNNSA appeared to be the most feasible and economic because it has rapid extraction rate, good phase separation, and high selectivity for Co and Ni over Al. Stripping of the loaded Ni and Co can be achieved by 0.5 and 1 M sulfuric acid and hydrochloric acid, respectively. However, smooth phase disengagement was not observed, which should be improved in future, for example by employing picolylamines with highly branched alkyl chains at tail position.

粉砕媒体の摩耗によって生ずる微量鉄分の瞬時溶解

In a grinding process, small amounts of iron are generally formed in the ground products. In the present study, the iron resulting from abrasion in wet grinding could be instantly oxydized by iron (III)-edta complexes (edta: ethylenediaminetetraacetic acid) in the presence of edta and oxygen to form iron (III)-edta. This iron-dissolving reaction was catalyzed by the iron (III)-edta complex, and was carried out more easily as the reaction proceeded. The final iron (III)-edta complexes were water-soluble and extremely stable.Consequently, the iron resulting from the abrasion can be eliminated completely by washing the ground products with water. In this study, the dissolutions of the iron attributed to the wear of a steel ball were mainly investigated in detail.

Bio‐optical properties in relation to an algal bloom caused by iron enrichment in the equatorial Pacific

In 1995 a massive bloom of phytoplankton composed primarily of diatoms was created by adding small quantities of iron to the surface waters of the equatorial Pacific. As part of this experiment, several bio‐optical parameters were measured using drifter instruments and shipboard measurements. The iron‐induced bloom resulted in dramatic changes in the bio‐optical properties of the study site, potentially resulting in light limitation of the phytoplankton at the peak of the bloom. The results also provide evidence for a shift in photosynthetic energy partitioning by the phytoplankton assemblage upon initial exposure to iron. It is unclear, however, whether the physiological changes associated with the bloom were purely a result of the iron addition, or were also influenced by changes in species composition. We hypothesize that iron‐induced changes in bio‐optical properties of equatorial Pacific waters could have far‐reaching effects on the global climate system.

A Mössbauer investigation of phases formed in Al-Fe alloys

During the semi-continuous casting of aluminium alloy ingots, the solidification rate varies substantially with position in the ingot. For commercial purity alloys, which contain small amounts of iron and silicon, intermetallic phases are formed inter-dendritically from the final liquid to solidify, and comprise typically 1% of the microstructure. The development in the work reported in this paper is that the phases of interest have been extracted from super-purity based, Bridgman Grown model aluminium-iron binary alloys by dissolving the aluminium matrix in butanol. This has the advantage of providing the pure phase and thus increases the proportion of iron (and Fe-57) which gives an improved signal to noise ratio for Moessbauer spectroscopy. Using phases extracted in this way, detailed variable temperature Moessbauer studies have been carried out on Al{sub 13}Fe{sub 4} and Al{sub 6}Fe. The variation with temperature of the isomer shift and absorption area were obtained. This enabled the recoil-free fractions of the two phases to be determined. With this information it was then possible to determine the proportion of Al{sub 13}Fe{sub 4} and Al{sub 6}Fe in an extracted sample containing both phases, and in a rod of the aluminium containing both phases in situ.

Extraction and selective stripping of molybdenum(VI) and vanadium(IV) from sulfuric acid solution containing aluminum(III), cobalt( II), nickel(II) and iron(III) by LIX 63 in Exxsol D80

5,8-diethyl-7-hydroxydodecane-6-oxime (LIX 63), a commercially available reagent, has been used in this work to investigate the extraction of molybdenum(VI) and vanadium(IV) from sulfuric acid solution in the presence of various other metals, such as aluminum(III), cobalt(H), nickel(II) and iron(III). Molybdenum(VI) and vanadium(IV) were extracted preferentially and separated completely from the coexisting metals involved at low pH (e.g., around 1.5) with LIX 63 dissolved in Exxsol D80. Vanadium(IV) in the loaded organic phase was selectively stripped by contacting with a 2 M sulfuric acid solution and isolated from molybdenum(VI). Molybdenum(VI) in the organic solvent, after the removal of vanadium(IV), was easily stripped by employing an aqueous ammonia solution as stripping agent and excellent phase separation performance (rapid phase separation, no formation of a second organic phase and no generation of an emulsion) in the stripping process was observed in all cases. A special emphasis, at least as an example of potential application, has been put on the extraction recovery of molybdenum(VI) and vanadium(IV) with LIX 63 extractant from the acidic sulfate liquor containing a sufficient quantity of aluminum(III), an appreciable amount of cobalt(II) and nickel(II), as well as a small amount of iron(III), resulting from the sulfuric acid leaching of spent hydrodesulfurization catalysts. The results obtained using the synthetic solution are in good agreement with those using the real leach liquor.

Catalytic synthesis of conductive polypyrrole using iron (III) catalyst and molecular oxygen

The catalytic oxidative polymerization of pyrrole was developed by the use of a relatively small amount of iron(III) salts as a catalyst and molecular oxygen as an oxidant. The reaction rate depended on the solvent used. Thus, the organic solvent with high dielectric constant gave the polymer with high electroconductivity at high yield. In contrast, both the polymerization rate and the conductivity of the produced polymer were low when the solvent with low dielectric constant was used. When propylene carbonate was used as the solvent with high dielectric constant, the turnover number reached about 10 in 96 h based on the charged amount of catalyst, and the highest electroconductivity around 10 −2 S cm −1 was achieved without extra doping. The addition of the quaternary ammonium salt to the reaction mixture improved the conductivity. Results on cyclic voltammetry suggested that the redox potential of iron ions depending on the solvent is an important factor to determine the efficiency of the catalytic polymerization of pyrrole.

Recovery of metal values from spent hydrodesulfurization catalysts by liquid-liquid extraction

The total dissolution of spent hydrodesulfurization catalysts in sulfuric acid yields an acidic solution containing a certain amount of rare metals like molybdenum, vanadium, cobalt, nickel, and a small amount of iron as well as an appreciable amount of aluminum. For the purpose of recovering the metallic values present in the solution, in the current work, the fundamental extraction characteristics of these metals with some typical commercial acidic organophosphorus compounds such as TR-83, PC-88A, PIA-8, and CYANEX 272 from the sulfuric acid media were investigated, and CYANEX 272 and PIA-8 were found to be suitable for selectively separating and recovering molybdenum and vanadium over the other metals from the specific solution at comparatively low pH. In addition, in order to further recover cobalt and nickel from the raffinate in the presence of a large excess of aluminum, a systematic investigation was conducted on the synergistic extraction behaviors of the mixed solvents consisting of LIX 63, an aliphatic α-hydroxyoxime extractant, and a series of acidic extractants such as CYANEX 272, PIA-8, PC-88A, D 2 EHPA, TR-83, and OPEHPA for cobalt, nickel, and aluminum. It was elucidated that all of these mixtures could exhibit a good synergistic effect for extraction of cobalt and nickel and that the lower the pK a of the acidic extractants, the greater the synergism. Contrarily, the extraction of aluminum, was considerably depressed by LIX 63. Using the difference in synergistic extraction performance between these metals, the effective extraction of cobalt and nickel away from aluminum was achieved from the sulfate solution at relatively low pH with the mixtures. In particular, the mixtures of LIX 63 in combination with CYANEX 272 or PIA-8 appeared to be the most feasible and economic from a practical point of view yielding acceptable separation efficiency for cobalt and nickel over aluminum and a low acidity requirement for stripping cobalt and nickel as well as negligible degradation of LIX 63. A full recovery processing route is proposed based on the experimental results.

Electrodes modified with synthetic clay minerals: Evidence of direct electron transfer from structural iron sites in the clay lattice

Clay-modified electrodes (CMEs) were prepared with synthetic smectite clays containing only one metal (magnesium, nickel or iron). A voltammetric wave was observed in the electrode modified with the iron clay in the absence of any adsorbed electroactive species. No such wave has ever been reported for natural smectites. It is attributed to direct electron transfer between redox-active structural Fe(II) sites in the clay lattice and the conductive substrate. This voltammetric wave was much larger when some nickel was incorporated in the lattice of the synthetic iron clay. The current obtained for a clay containing 14% nickel was more than six times larger than for the pure iron clay. However, no peaks were found for the pure nickel clay or for nickel clays containing small amounts of iron. The redox-active sites in the synthetic iron clay were shown to relay electrons between [Ru(NH3)6]2+ and [Fe(bpy)3]3+ cations coadsorbed in the CME, forming the beginning of an electron transport chain in the clay films. No evidence of mediated electron transfer was found for the iron-free magnesium clay. Variations of the Fe(II)Fe(III) ratio in films of natural smectites during cyclic voltammetry was also followed by UV-visible spectroscopy.

Laser desensitisation of the heat affected zone (HAZ) in austenitic stainless steels

Summary The aim of this work is to promote a basic knowledge of the phenomenon of sensitisation in the heat affected zone (HAZ) in austenitic stainless steels and provide information on a method of desensitisation using laser beams without impairing other types of corrosion resistance (pitting corrosion resistance). Sensitisation of the HAZ is caused by the formation, along the grain boundaries and twin boundaries, of a zone with lower chromium content due to precipitation of Cr23C6 which contains 70–80% Cr and small quantities of iron, and which has a cubic/cubic relationship with the austenite matrix. It was found that the usual morphology of the carbides was bar or globule shapes. With increased holding time, carbides in the form of coarse‐grained globules (idiomorphs) and in dendrite forms were also found. However, no significant variations in the composition of the carbides or in the width of the chromium‐depleted zone were observed to be due to morphology. Laser desensitisation can be achieved with ...